O’Malley is one of five candidates in a field dominated by Hillary Rodham Clinton, a former secretary of state.

Clinton, who began her campaign in mid-April, raised $45 million through the end of June. O’Malley’s bid began May 30, and his supporters contributed $2 million in 30 days.

Vermont Sen. Bernie Sanders raised $15 million, while former Rhode Island Gov. Lincoln Chafee is financing most of his campaign out of his own pocket. The fifth candidate, Jim Webb, a former Virginia senator, only recently became a candidate.

Most of the presidential contenders are due to file their initial fundraising reports to federal regulators by midnight Wednesday.